Method of manufacturing crystalline alumina.



UNITED STATES PATENT OFFICE.

FRANK J. TONE AND THOMAS B. ALLEN, OF NIAG AR A FALLS. NEW YORK.ASSIGNORS TO THE CAR-BORUNDUM COMIPANY. OF NIAGARA FALLS. NEW YORK. ACORPORA- TION OF PENNSYLVANIA.

METHOD OF MANUFACTURING CBYSTALLINE ALUMINA.

N0 Drawing.

1'0 (/7! 1177mm.- izf may concern:

lie it known that we, FRANK J. Tom: and 'l'nou.\s l3. Amen. bothresidents of Niagara Falls. in the county of .\'iagara and State of NewYork. have invented the Method of Manufacturing Crystalline Alumina; ofwhich the following is a specitication. 4

)ur invention has relation to crystalline almuina and improvement in themanufacture thereof: and is designed to provid a fused crystallinealumina which contains but a very small percentage of the metallit'erousoxid used in its produt'ition, and which is substantially free fromsuboxid or carbid of aluminum or other impurities, and which willpossess other advantages hereinafter pointed out.

, ()ur invention is also designed to provide a method of producing thismaterial which caube carried out in an etlicicnt and economical manner.

The smelting of any aluminous ores, such as bauxite, emery. l-zaolin,and clay, in order to obtain pure alumina. is accompanied by manyditliculties. It has been sou ht: in various ways to prepare a pure cry;alline alumina having refractory and abrasive properties by performing adifferential reduction with carbon on the aluminous ores abovementioned. If bauxite or emery be sliielted with carbon, it is possibleto reduce the oxids of iron and silicon in a substantially completemanner, but it is impossible to remove the oxid of titanium withoutreducing the alumina. As bauxite and emery contain from three to fourper cent. of Oxid of titanium, it is substantially impracticable toproduce in this mannea stable crystalline alumina having more than 97 to98%,

alumina.

@It' kaolin or clay be smelted with carbon, ibhas been found possible toproduce a very pure product having over 99']; alumina. as these orescontain practically no titanium oxid; but as they contain from to (30;

of silica. a large addition of iron oxid or other similar oxid must bemade in order to' reduce them elliciently; and it has been found veryexpensive and inetlicient to carry out- .the production of pure aluminain this manner.

A Well-known method of carrying out the Specification of Letters Yatent.

Patented Nov. 12. 1912.

Application filed August 30, 1911. Serial No. 646,862.

purification of impure aluminous ores. is by solution in a causticalkali. and after filterine' olt' the in'ipuritics. subsequentlyprecipitating. preferably by the Ilse of carbon dioxid. By this method.it is possible to produce a very pure form of alumina. which is.however. in an amorphous condition. if this pure alununa be melted In anelectric turnacc. it will absorb carbon from the furnace hearth andelectrodes: and while the.

product consists of crystalline alumina. it

contains reduced alumina in the form of thein sutlicient quantity todestroy any carbidor snboxid of aluminum that is formed. we can obtain a(l)ifiitllllll! product consisting of substantially pure aluminacontaining less than one-half of one per cent. of metalliferous oxid.

\l'e will now proceed to describe the manner in which we prefertopractice our invention. using iron oxid as a suitable material toprevent the formation of aluminum cal-bid or suboxid, although. as ab vedc scribed, other easily reducible metalliferous oxids' such asmanganese oxid may be em ployed. Iron oxid has the advantage of beinginexpensive. while the metallic iron has a high magnetic susceptibilitywhich renders its removal from the crystalline alumina a relativelysimple matter.

\Ve take substantially pure amorphous alumina and add thereto about tenper cent. of iron oxid. This mixture is fed into an electric furnace.which is preferably. although not necessarily. of the type dcscribcd inU. H. latcnt to Frank J. 'lonc (one of the present applicantsiXo.929.517, dated July 27. 190i. \Ve prefer to operate the process on theresistance principle of heating. the charge forming a conducting patl:between the furnace electrodes, as we believ the. formation of thereduction produntil the product is in solid form.

ucts of alumina is more easily prevented by this method. The mixture isgradually fed into thefurnace until the furnace crucible is tallinealumina containing from one-tenth to five-tenths er cent. of iron oxid,and substantially ree from reduced alumina either in the form ofmetallic aluminum or suboxid' or carbid of aluminum. The prescues ofthis. amount of metalliferous oxid im urity gives the product valuablephysiptope'rties and distinguishes it from products having a higherpercentage of imurities. Our Improved product has a less 0 oftoughnessand greater hardness; an on account of this altered ratio of toughmassto hardness, it is much better adapted for 'useas an abrasive in certaingrinding operatiohs and in metal cutting. The presence of this amount-ofoxidized impurities also insures the absence of reduction prodnets, andthus contributes to the stability and non-distintegrating properties ofthe 'product, and which are properties not posaessed 1n the same degreeby the fused lumina of higher purity. By reason of the absence offluxing impurities in any substantial amount, the product also possessesvaluable refractory qualities.

We do not desire to limit ourselves to the precise method of carryingout our invention hereiiidescribed, asanany changes may be made in thedetails thereof by those skilled in the art withoutdeparting from thespirit and scope of our invention, as defined in the appended claims.

We claim 2- v 1. In the manufacture of crystalline alumina, theimprovement which consists in portion of the oxid to metallic form andfusing the alumina.

2. In the manufacture of crystalline alumina, the improvement whichconsists in melting a mixture of pure alumina with sufficientmetalliferous oxid to prevent the formation of reduction products ofalumina.

In the manufacture of crystalline alumina, the improvement whichconsists in melting a mixture of pure alumina with sutlicientmetalliferous oxid to revent the formation of carbid or SllbOXlt ofalumi:

num.

4. In the manufacture of crystalline alumina, the improvement whichconsists in melting a mixture of pure alumina with sufiicient ironoxidto prevent the formation ofany reduction products of alumina.

In the manufacture of crystalline alumina. the improvement whichconsists in melting a mixture of pure amorphous alumina with sufficientiron oxid to prevent the formation of carbid or suhoxid of alumi num.

(i. In the manufacture of crystalline alumina, the improvement whichconsists in melting ure amorphous alumina with an easily re ucible oxid,and reducing the major portion of the oxid to thereby produce a fusedalumina containing not less than onetenth per cent, nor more thanfive-tenths per cent., of the said metallifcrous oxid and which issubstantially free from other impu 'ities.

' t. In the manufacture of crystalline alumina. the improvement whichconsists in forming a conductive charge of pure amorphous alumina andmetalliferous oxid between the electrodes of an electric resistancefurnace, and reducing the major portion of the metalliferous oxid,thereb producing a fused alumina containing not ess than onc tenth percent, nor more than five-tenths per cent, of the said oxid, and which issubstantially free from other impurities.

In testimony whereof, we have hereunto set our hands.

FRANK J. TONE. THOS. B. ALLEN. \Vitnesses as to Frank J. Tone:

Passco'rr SIMPSON, A. S. Bxxmioxi. \Vitnesses as to Thomas B. Allen:

Faro I. PIERCE, C. H. Gnnnnwooo.

